Method of using a sliding surface material for seals or bearings



y 1963 J. F. CERNESS ET AL 3,096,565

METHOD OF USING A SLIDING SURFACE MATERIAL FOR SEALS 0R BEARINGSOriginal Filed Dec. 21, 1956 VII/III,

i& 1 ii VII/1! F l G .I

F I G .3 INVENTORS JOSEPH F. CERNESS BY DOUGLAS H. STRONG TORNEY UniteStates Patent 3,096,565 METHOD OF USING A SLIDING SURFACE MA- TERIAL FORSEALS OR BEARINGS Joseph F. Cerness, East Cleveland, and Douglas H.

Strong, Willoughby, Ohio, assignors to Clevite Corporation, Cleveland,Ohio, a corporation of Ohio Continuation of abandoned application Ser.No. 629,936, Dec. 21, 1956. This application Apr. 10, 1959, Ser. No.805,480

3 Claims. (Cl. 29-1495) This invention pertains to a method of using aparticular material in sliding surface engagement, particnlarly for aseal, a sleeve bearing, a bushing, a piston ring, a valve guide or thelike. This is a continuation of our prior patent application, SerialNumber 629,936, filed December 21, 1956, for Sliding Surface MaterialEspecially for Seals or Bearings, filed in the names of Joseph F.Cerness and Douglas H. Strong, which prior application is now abandoned.

For a number of years there has been a critical need for an improvedsliding surface bearing and seal material which will withstand hightemperature operation as well as low temperature operation, and whichwill withstand the thermal shock incident to starting cold (about 67 F.)and warming up to a high ambient temperature in a time period of aboutone minute, and which will thereafter run for a long period of time atthe elevated temperature, particularly in the absence of externallyapplied oil or grease. These criteria, coupled with the otherrequirements for a good seal and bearing material have resulted in many,many diffenent materials failing to perform satisfactorily.

The use of the material of the present invention fulfills to a verylange degree all of the requirements for both a sliding surface sealmaterial and a sliding surface bearing material, and is admirably suitedto high temperature operation starting from a temperature well belowzero, with and without external lubrication.

An object of the invention is the provision of a new method of using aparticular material as an improved sliding surface material, preferablyfor operation against a similar material, and in some instances againsta dissimilar material, particularly in the high temperature range butcapable of starting at temperatures well below F.

Another object of the invention is the provision of a method of using asliding surface material, such as a seal or bearing material, which istough, resists Wear and corrosion, which resists thermal shock, 'whosethermal expansion approximates that of steel, whose heat conductivity isgood, whose porosity is low, and which is inexpensive and can bemachined, which has to a certain degree the ability to imbed dirtparticles, which will operate for short periods of time at very lowtemperatures, and which will withstand long periods of operation inambient temperatures of about 1100 F., all of the above without externallubrication, and which is also suitable for use with externallubrication.

A further object of the present invention is the provision of a methodof using a sliding surface material which will withstand a number of lowtemperature starts and which will operate continuously at temperaturesabout 1100 F. Without external lubrication.

Still another object of the invention is to provide a method of using asliding surface material, particularly 3,096,565 Patented July 9, 1963"ice in engagement with similar material, over a short period of time inan ambient temperature of 1200" F. without external lubrication.

For a better understanding of the present invention, together with otherand further objects thereof, reference is bad to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

In the search for better seal materials a list of ten desirableproperties has been used as a criterion to judge the relative merits ofthe materials tested. The desirable properties are as follows:

(1) Wear resistance: preferably the material should not wear at all, butif it does it should wear at a low, uniform rate and it should not gallor seize.

(2) Toughness: the material should be strong without brittleness sinceexcessive fragility hampers engine assembly as well as increasing theprobability of operating failure.

(3) Corrosion and oxidation resistance: the material should resistoxidation and corrosion by air, oil and fuel products even at sustainedhigh temperatures.

(4) Thermal shock resistance: the material must resist fracture ordamage by extremely fast heating rates found in gas turbine engines.

(5) Thermal expansion of the material should match as closely aspossible the expansion rates of its surrounding parts, such as the shaftand housing.

(6) Heat conductivity should be good to conduct away the heatestablished by friction in the seal and to maintain the seal temperatureas low as possible even at very high surface speeds.

(7) Weight: should Weigh as little as possible weight is at a premium inaircraft.

(8) Porosity: should be as low as possible.

(9) Machinability: should be machinable by standard practices.

(10) Economics should be moderate in cost and contain no strategicmaterials.

It will be seen from this list that the requirements for a \good sealmaterial are quite severe.

In the past one of the best combinations for a gas turbine oil seal hasbeen chrome plate operating against carbon graphite materials. Thiscombination, however, has had important limitations which restrict itsuse in present and future aircraft. The carbon-graphite lacks oxidationresistance when operated above 700- to 800 F., and it is quite fragileand brittle. Also, the chrome begins to soften at temperatures about 500F. In spite of this, and because better materials have been lacking, thecarbon-graphite chrome seal has achieved considerable success eventhough it is quite expensive to fabricate, due in part to thebrittleness of the carbon-graphite.

An outstanding use has been discovered for a material which to a verylarge degree fulfills all of the ten requirements of a good hightemperature seal material, and which, in addition has to a very largedegree several extra properties which make it admirably suited as asliding surface bearing material particularly for use at temperaturesabove about 600 F. This material, when rubbed against itself has a verylow coefficient of friction, with and without external lubrication, andhas to a certain degree the ability to imbed dirt particles. 7

Its low coefficient of friction when rubbed against itsince self is agreat advantage in a seal material since in a gas turbine the highsurface speeds of the seal tend to generate considerable heat, and ofcourse the lower the coefiicient of friction the less heat is generatedand the less power is consumed.

This outstanding sliding surface material consists essentially of thefollowing:

Percent Carbon about .87 Silicon about .25 Manganese about .25 Chromiumabout 4.00 Vanadium about 1.90 Molybdenum about 8.00 Iron BalanceSliding surfaces made of the above material have been successfullytested sliding against similar surface material in dry air, and withoutexternal lubrication. The relative surface speed of two engaging partsduring the test was 156 feet per second; loading between the rubbingsurfaces was 18 pounds per square inch; and ambient temperatures rangedup to 1200 F. with the sliding surface temperatures ranging from 800 F.to 2000 F.

The outstanding combination for sliding surface contact at hightemperatures, for seal or bearing application, was achieved by a pieceof the aforedescribed material machined from annealed stock rubbingagainst a piece of the same material. This combination operated 5 hourscontinuously at ambient temperatures of 1100 F. or slightly higher, withsurface contact temperatures reaching 1350 F. or slightly higher. Nolubricating material was used, other than the inherent lubricatingability of the material itself. The average wear of the two relativelyrotating parts due to friction was only .0004 inch per hour over the5-hour period, and the average coefficient of friction was .06. It isconsidered that this is an outstanding performance.

In another substantially similar test the ambient temperature was 1200F., and it is estimated that the temperature of the rubbing surfacesreached about 2000 F. The average coetficient of friction was .07; wearon the rotor varied from a pickup of .0008 to a loss of .0008, and thestator tended to pick up material from the rotor. Under these extremeconditions the material operated successfully for about 30 minutes,suflicient for many present day one-shot devices.

A test run with the same material but hardened to Rockwell C 50-55, atan ambient temperature 820 F. and with surface contact temperature of1200 F., showed an average wear rate of only .00065 inch per hour over a5- hour test, and an average coefficient of friction of .057. Both ofthese aforesaid tests were without external lubrication.

A test run with the hardened material in contact with the unhardened, orannealed, material showed a satisfactory wear rate for both parts, butthe average coefiicient of friction was about twice the averagecoefficient of friction when the annealed material was rubbed againstitself or the hardened material was rubbed against itself.

Since the sliding surface material of this invention is an iron basealloy containing about 85% iron, its coeflicient of thermal expansionvery closely matches the coefiicient of thermal expansion of itssurrounding steel parts. It is basically a tough tool steel, but can bemachined with carbide tools. No strategic metals are in the alloy andits heat conductivity, while not extremely high, is satisfactory. It isnot porous, its density is moderate, but because it is non-porous,strong and tough, a smaller amount of this new material will replace alarge amount of presently used carbon which is relatively weak and quitebrittle. Consequently, even in aircraft use the greater density of thismaterial compared to carbon is considered to be inconsequential.Outstanding characteristics of this new sliding surface material are itswear resistance, its low coefficient of friction against itself atelevated temperatures, its toughness and its abiity to withstandphysical abuse and extreme thermal shock, and its ability to operatewithout external lubrication. To date it has shown quite good resistanceto oxidation and corrosion at elevated temperatures over modest testperiods, but in the event this quality proves to be lower than desired,in some applications coatings of known corrosion and oxidation resistingmaterials may be applied to the non-sliding surface portions thereof.All of these factors, taken in conjunction with the cost of thismaterial which, when machined into finished seal and sliding surfacebearing parts, is low compared to present day materials, indicate thatthis is a most outstanding material, one which will greatly reduce thecost of present day seals and which will extend their temperature rangeconsiderably, and which will greatly extend the temperature range ofsliding bearings.

With reference to the single sheet of drawing there are shown several ofthe typical sliding surface uses of the material .of this invention. Inaddition, other sliding surface uses such as piston rings, the bore of acylinder etc., may be thought of.

In FIGURE 1 there is shown a seal between a rotating shaft 10 and astationary member 11. A sliding surface bearing 12 is located betweenthe relatively rotating parts, and the seal device is shown generally bythe reference character 15.

The seal 15 comprises a ring 16 secured in tight relationship to theshaft 10 and made of the material of this invention. Member 16 rotateswith the shaft 10.

A cup-shaped member 17 is held fixed with respect to the stationarymember 11 by means of the flanged ring 18 and it carries severallocating pins 20, 21. Member 17 may be made of the material of thisinvention because of thermal expansion problems, but it is notessential.

Three sealing rings 23, 24 and 25 are mounted between the ring 16 andthe cup-shaped member 17. Each of these rings is formed of the materialof this invention. Ring 23 is mounted around ring 24, radially outwardlytherefrom, and ring 24 is mounted in sealing engagement with the ringmember 16. Relative rotation takes place between rimg member 16 and thesealing ring 24.

The ring 23 is pinned to the cup-shaped retaining mem-t ber 17 by pin21, and sealing ring 24 is pinned by pin 20 so that they are constrainedagainst rotation. Each of these sealing rings 23, 24 has an expansiongap into which the pins extend, thereby preventing relative rotationbetween the sealing rings with consequent lining up of the expansiongaps to the detriment of the seal.

Sealing ring 25 is placed axially adjacent sealing rings 23, 24 and hasan expansion gap into which the pin 21 extends. A retaining ring 28 isheld against ring 25 by spring 29, and a snap ring 30 secured to member17 holds the spring in place. Garter springs 31 hold the sealing rings23, 24, 25 in sealing engagement against the ring 16. Relative rotationtakes place between the seal 15 and the ring 16. Consequently the partsthereof which are in contact with a relatively rotating member should bemade of the material of this invention. They are the ring 16 secured tothe shaft 10 and the sealing rings 23, 24 and 25.

FIGURE 2 shows a flanged sleeve bearing, and FIG- URE 3 a valve guidemade of the material of this invention.

While the method of the present invention reaches its greatestusefulness and its most outstanding qualities when the sliding surfacematerial is rubbed against itself, the method may also be practiced byrubbing the material, with or without external lubrication, againstmaterials such as nitrided steel, carburized steel, ductile iron, or SAE52100 which is a known steel material consisting of 1.3 to 1.6%chromium, .95 to 1.1% carbon, .2 to 35% silicon, .25 to .45% manganese,and a maximum of about 025% phosphorus and .025 sulphur.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

We claim:

1. The process of making a sliding surface seal or bearing whichcomprises the step of forming a body of an alloy consisting essentiallyof:

Percent Carbon .87

Silicon .25 Manganese .25 Chromium 4.00

Vanadium 1.90 Molybdenum 8.00 Iron Balance and forming on said body asurface for rubbing engalgement with another body.

2. The process as set forth in claim 1 further characterized by formingsaid other body of an alloy consisting essentially of:

3. The process as set forth in claim 1, funther characterized by formingsaid other body of material selected from the group consisting of SAE52100, nitrided steel, oarburized steel and ductile iron.

References Cited in the file of this patent UNITED STATES PATENTS1,747,394 Scott Feb. 18, 1930 2,086,681 Scott July 13, 1937 2,325,088Wright July 27, 1943 2,592,277 Hammer Apr. 8, 1952 OTHER REFERENCES ToolSteels by James Presley Gill et 211., published by A.S.M., Cleveland,Ohio, 1944.

Metal Handbook A.S.M. (1948).

Metal Progress A.S.M. (1948

1. THE PROCESS OF MAKING A SLIDING SURFACE SEAL BEARING WHICH COMPRISESTHE STEP OF FORMING A BODY OF AN ALLOY CONSISTING ESSENTIALLY OF: